1. Field of the Invention
A present invention relates to a pressure wide-mouth container made of a synthetic resin and a method of manufacturing the pressure wide-mouth container. More particularly, the present invention relates to a container which is used to store tennis balls under pressure. To seal the container, a flange portion is projected from the periphery of a wide mouth of the container having a diameter almost equal to that of the cylindrical body portion thereof. A lid made of metal is tightened against a flange portion, with the lid doubly covering the flange portion.
2. Description of the Related Art
As a container containing an object such as tennis balls desired to be stored under pressure, a metal can made of a metal material has been used. In recent years, instead of the metal can, there is the wide use of a container made of a synthetic resin manufactured by blow-molding a synthetic resin such as polyethylene terephthalate or the like.
In using a container made of a synthetic resin, such as a pressure container for storing tennis balls or the like under pressure, similarly to the metal can, it is necessary to put the object in the container under pressure, close the container by tightening the metal lid against the flange portion projecting from the edge of the opening of the container, with the flange portion being doubly covered with the lid, and sealing the inside of the container under pressure.
A container made of the synthetic resin is much less expensive than a metal can in material cost. However, since a container made of a synthetic resin is produced by using a biaxial drawing and blow molding operation, it is difficult to provide the container with the flange portion which can meet the high strength requirement of withstanding the pressure to be applied thereto from the lid which is doubly tightened against the flange portion.
In order to solve the above-described problem, a container manufactured by the process shown in FIGS. 8A through 8D is proposed in Examined Japanese Patent Publication No. 6-22859. According to the container, as shown in FIG. 8A, there is formed by injection molding a parison 1 having a closed bottom surface 1a, an opening 1b at its top, and a cylindrical body portion 1c long and small in its diameter. Then, as shown in FIG. 8B, the parison 1 which is a molded product of a primary process is transferred to a blow molding die 2 to draw it in a biaxial direction (X and Y-directions) to obtain a molded product 3 of a secondary process, as shown in FIG. 8C. The semi-finished product 3 is cut along a line L to remove an umbrella-shaped part 1d formed at the upper end thereof. A container 4 shown in FIG. 8D is a final product.
The container 4 formed by blow molding has a cylindrical body portion 4a; a wide mouth 4b open at one end of the body portion 4a and having a diameter substantially equal to that of the body portion 4a; a flange portion 4c projecting radially from the periphery of the wide mouth 4b; and a bottom portion 4d formed at the other end of the body portion 4a. After tennis balls are put in the container 4 from the flange portion 4c, a lid 5 is tightened against the flange portion 4c, with the lid 5 doubly covering the flange portion 4c, as shown in FIG. 9 to seal the interior of the container 4. In this manner, tennis balls are stored in the container 4 under pressure.
In the method shown in FIG. 8, for manufacturing a container having the flange portion 4c against which the lid 5 is doubly tightened, the semi-finished (secondary) product 3 shown in FIG. 8C is formed by molding. Then, it is necessary to perform the additional process step of cutting off the unnecessary umbrella-shaped part 1d formed at the upper end of the body portion 4a. Thus, the method shown in FIG. 8 has comparatively many process steps.
In addition to the above-described problem, if the degree of the size accuracy of he flange portion 4c is low, a gap is generated between the flange portion 4c and the lid 5 which is doubly tightened against the flange portion 4c. Thus, the container 4 has a low degree of sealing performance. To prevent this, it is necessary to allow the flange portion 4c to have a high degree of size accuracy in the cutting operation. To this end, it is necessary to use a particular cutting tool having a high degree of cutting accuracy such as a ring-shaped cutter and perform the cutting step at high accuracy. Consequently,the method shown in FIG. 8 causes the manufacturing cost to be high and the manufacturing time to be extended.
Moreover, to form the flange portion 4c with a high size accuracy, it is necessary to minimize the variation of the thickness thereof. However, to allow the thickness thereof to be uniform in the biaxial drawing and blow molding operations, stability in the molding technique and molding condition and the operation stability of the molding machine are demanded. However, it is not always easy to keep these factors stable. In particular, the flange portion 4c requires a thickness of less than 1 mm. Thus, defective products are likely to be produced in the blow molding process. Actually, many defective articles are produced.
Furthermore, in the process of the formation of the flange portion 4c, the umbrella-shaped portion 1d formed at the upper end of the body portion 4a is cut off and discarded. That is, a part of the material is wasted. It is conceivable that the umbrella-shaped portion 1d can be recycled by mixing it with a resinous material. However, in this case, it is necessary to pulverize the umbrella-shaped portion id before mixing it with the resinous material with a pulverizing machine. Further, there is a limitation in the mixing percentage in consideration of the stability in the molding of the mixed materials. Thus, it is difficult to recycle the umbrella-shaped portion 1d. 
Furthermore, when the container is used to accommodate tennis balls, the container is exposed to a high temperature atmosphere of the trunk of a vehicle or the like for a long time. Because the flange portion 4c is thinly formed by blow molding, it can become deformed by heat. As a result, gaps can be formed between the flange portion 4c and the lid 5 permitting air to leak out from the interior of the container 4. Thus, it is impossible to hold the interior of the container under pressure and hence hold the tennis balls therein at a predetermined internal pressure.
The present invention has been made in view of the above-described problem. Thus, it is an object of the present invention to provide a pressure wide-mouth container made of a synthetic resin and material and having a flange portion against which a lid is tightened, with the lid doubly covering the flange portion and which has a precise dimensional accuracy and a high degree of strength to seal the interior of he container under pressure.
It is another object of the present invention to manufacture a container in a minimum number of process steps and without generating waste.
In order to achieve this object, there is provided a pressure wide-mouth container made of a synthetic resin and having a cylindrical body portion, a flange portion projecting from the-periphery of the wide mouth formed at one end of the body portion; and a bottom portion closing the other end of the body portion. Advantageously, the flange portion and a peripheral portion of the wide mouth are formed by injection molding and not drawn after the injection molding is carried out. The body portion except for the peripheral portion of the wide mouth and the bottom portion are formed by injection molding and drawn by blow molding to be performed after the injection molding is carried out. The bottom portion is drawn at a lower drawing ratio than the body portion.
As described above, the flange portion and the peripheral portion of the wide mouth continuous with the flange portion are formed by injection molding. In the conventional manufacturing method, it is necessary to cut off the upper end of a semi-finished product after blow molding is carried out as shown in FIG. 8, whereas the manufacturing method of the present invention makes it possible to elimnate the cutting process and the disposal problem. There is no variations n the thickness of the pressure wide-mouth container in the blow molding operation and no variations in the size thereof because no cutting step is performed. Because the pressure wide-mouth container is formed by using a mold, it is possible to hold the thickness of the flange portion or the like to a predetermined precise dimensional accuracy. Consequently, a gap is not generated between the flange portion and the lid which is doubly tightened against the flange portion. That is, it is possible to securely seal the interior of the container under pressure.
Further, the bottom portion is drawn at a lower drawing ratio than the body portion to make the thickness of the bottom portion larger than that of the body portion. Thus, when the internal pressure of the container is applied to the bottom portion, the bottom portion is not easily deformed.
The diameter of the wide mouth is substantially equal to that of the body portion. The thickness of the flange portion and that of the peripheral portion of the wide mouth are set to be larger than the thickness of the body portion to permit the strength of the flange portion and the peripheral portion of the wide mouth to be higher than that of the body portion so that the periphery of a lid made of metal can be doubly tightened against the flange portion.
In the conventional container formed by blow molding shown in FIG. 8, the flange portion is drawn to allow it to have a comparatively high rigidity so that the flange portion may withstand the pressure to be applied thereto from the lid which is doubly tightened against the flange portion. In the present invention, the flange portion is only formed by injection molding and thus is not drawn. Thus, the rigidity of the flange portion is not increased by the blow molding (drawing). Supposing that the thickness of the flange portion not drawn is equal to that of a drawn one, the flange portion not drawn is lower than the drawn flange portion in the strength for the pressure to be applied thereto from the lid which is doubly tightened against the flange portion. Therefore, the thickness of the flange portion of the present invention, formed by injection molding and not drawn, is set to be larger by 30% to 50% than that of the flange portion formed by blow molding.
In the present invention, the thickness of the flange portion which is formed by injection molding and is not drawn is favorably 1-5 times and more favorably 1.5-3 times as large as that of the body portion formed by injection molding and blow molding (biaxial drawing). The thickness of the peripheral portion of the wide mouth continuous with the flange portion is larger than that of the flange portion and 5-8 times as large as that of the body portion formed by the injection molding and the drawing. More specifically, in case that the container is used to accommodate tennis balls, the thickness of the flange portion is set to 0.4 mm-0.8 mm, favorably, 0.4 mm-0.6 mm, and more favorably, 0.55 mm. The thickness of the peripheral portion of the wide mouth is set to 1.0 mm-1.5 mm. The thickness of the body portion formed by injection molding and the drawing is set to 0.2 mm-0.4 mm, and favorably, 0.2 mm-0.35 mm. The width (projection amount from the peripheral portion of the wide mouth) of the flange portion is 2-5 mm, favorably, 2-4 mm, and more favorably, 3 mm. The length of the body portion in its axial direction depends on the object to be accommodated in the container. When the container is used to house tennis balls, the length of the body portion is set to contain 2-4 tennis balls. When the container contains four tennis balls, the length thereof is set to 265 mm.
The bottom portion has a flat plate-shaped hollow portion or a dome-shaped hollow portion formed in a center of the bottom portion and an erected ring portion formed on a periphery of the hollow portion. Otherwise, the bottom portion has a plurality of hollow portions formed circumferentially at certain intervals and a plurality of erected portions projecting from the intervals such that the shape of the bottom is petaloid. The bottom portion is so shaped that when an internal pressure is applied to the container, the hollow portion does not project beyond the erected ring portion to allow the container to maintain a self-standing configuration.
As described above, the bottom portion is drawn at a lower drawing ratio than the body portion. Thus, the thickness of the bottom portion is larger than that of the body portion and thus the bottom portion has a higher strength than the body portion. Accordingly, when the internal pressure is applied to the bottom portion, the bottom portion is not easily deformed. Further, the bottom portion has the erected ring portion or the petaloid portion to allow the container to have a pressure-resistant construction, such that the shape of the bottom portion prevents the hollow portion from projecting outwardly. The shape allows the container to stand for itself.
The container is preferably formed of molded polyethylene terephthalate. The container may be formed of synthetic resin such as polyvinyl chloride.
The container is preferably used to contain a tennis ball having a predetermined internal pressure; with a lid made of metal covering a flange portion doubly, a periphery of a metal lid is doubly tightened against a flange portion of the container under pressure to seal the container and store the tennis ball in the container under pressure.
Further, in the present invention, there is provided a method of manufacturing a pressure wide-mouth container made of synthetic resin comprising the steps of forming a cylindrical parison by injection molding, with a bottom surface thereof closed, a top thereof formed as a wide mouth, and a flange portion projecting from a periphery of the wide mouth; and drawing portions of the parison, except for the flange portion and the peripheral portion of the wide mouth, by biaxial blow molding to form a body portion and a bottom portion such that the bottom portion is drawn at a lower drawing ratio than the body portion.
More specifically, the parison is formed by injection molding as a bottom surface-closed conic cylindrical semi-finished product having a wide mouth and a flange portion projecting outward from the peripheral portion of the wide mouth. The parison becomes smaller gradually in its diameter from the peripheral portion of the wide mouth toward the bottom portion. The parison is transferred to a biaxial blow mold in which the flange portion and the peripheral portion of the wide mouth are brought into close contact with the surface of a cavity to prevent them from being drawn. Pressurized air is blown into the parison from the wide mouth to draw the conic cylindrical parison in a biaxial direction (X and Y-directions). Consequently, the parison is expanded such that in the X-direction, the diameter of the body portion is expanded to a diameter approximately equal to that of the wide mouth and in the Y-direction, the height of the parison becomes a predetermined one. In the blow molding, the shape of bottom portion is as same as a shape of a surface of the cavity or that of a member inserted in the cavity.
In the method of the present invention, the flange portion and the peripheral portion of the wide mouth continuous with the flange portion are formed only by injection molding; and the body portion and the bottom portion are formed by the injection molding and the blow molding (drawing in biaxial direction). The method of the present invention eliminates the need for a cutting process required to form the flange portion, thus manufacturing the container in a smaller number of process steps. That is, the method allows the container to be manufactured at a high productivity and at a lower cost.